Heretofore, phase difference detection AF has been known as an AF method which is adopted in a digital camera or the like. In the phase difference detection AF, a distance to a subject is obtained on the basis of correlation calculation about pixel signals obtained from pair of pixels for phase difference detection which are arranged on a solid-state image pickup element such as a CMOS image sensor, and focus is controlled on the basis of the resulting distance.
In addition, heretofore, some solid-state image pickup elements have adopted a column ADC system (referred to as a line sequential ADC system as well) in which in converting analog electrical signals read out from the respective pixels into digital signals, the pixels belonging to the same column hold an ADC (Analog Digital Converter) in common, and a plurality of ADCs corresponding to the respective columns is operated in parallel to each other.
In the column ADC system, although in a stage in which the AF is carried out, the exposure and the reading are carried out at the same timing for the pixels (including the pixels for phase difference detection) arranged in the same row, the exposure and the reading for the rows are sequentially carried out. Therefore, in the case where the pixels different in rows from each other in which they are arranged are compared with each other, the timings of the exposure and the reading shall be shifted.
An area ADC system is also present with which a difference in timing of the exposure and the reading can be shortened as compared with the column ADC system described above. In the area ADC system, all the pixels are divided into pixel blocks each having a size of several pixels×several pixels, the ADC is shared in units of the pixel blocks, and a plurality of ADCs each corresponding to each of the pixel blocks, is operated in parallel to one another (for example, refer to PTL 1).